1. Field of the Invention
The present invention relates to a vibration wave motor utilizing a travelling vibration wave.
2. Related Background Art
A vibration wave motor utilizes, in its driving operation, a vibration energy generated when a frequency voltage is applied to, e.g., a piezo-electric element. The vibration wave motor has a simple and compact structure as compared to a conventional electro-magnetic motor since it requires no windings, and can obtain a large torque at a low rotational speed. The vibration wave motor is also called an ultrasonic wave motor, and a motor which generates a vibration wave as a travelling wave is put into practical applications as, e.g., a motor for driving an auto-focus lens of a single-reflex lens.
The principle of the driving operation of this travelling wave type vibration motor is known to those who are skilled in the art, as disclosed in, e.g., Japanese Laid-Open Patent Application No. 62-260567. That is, AC voltages having different phases as a function of time are applied to driving piezo-electric elements of two phases, i.e., A and B phases having different spatial phases, thereby exciting standing waves having a phase difference of 90.degree. in an elastic member to which the piezo-electric elements are bonded. These standing waves are synthesized to form a travelling wave. A moving member urged against the elastic member is frictionally driven by this travelling wave.
FIG. 6 is a sectional view of a conventional travelling wave type vibration wave motor.
In FIG. 6, known piezo-electric elements 11a are adhered to a bottom surface of a ring-shaped elastic member 11 mainly formed of a metal, thus constituting a vibration member. A plurality of projections 11b are formed on the elastic member to increase an amplitude of vibration in a feed direction.
A ring-like moving member 2 is urged against the upper surface of the elastic member 11, and has a frictional member 2a, an anti-vibration member 2b, an anti-vibration member receiving member 2c, and a bearing member 2d. An end portion of the frictional member 2a is in contact with the upper surface of the elastic member 11, and the anti-vibration member 2b contacting the frictional member 2a is formed of an elastic material such as butyl rubber having good vibration damping characteristics.
The anti-vibration member receiving member 2c is also a ring-like metal member, and is fixed to the ring-like bearing member 2d by a screw 2e.
A fixing portion 3 rotatably holds the moving member 2 using bearing members 4 and 5 through balls 15.
The other surface of the elastic member 11 contacts a pressing ring 9 via a vibration insulating member 6 such as felt, a holding plate 7, and a belleville spring 8 for urging the elastic member 11 against the moving member 2.
Note that the operation of the vibration wave motor for moving the moving member 2 by a travelling vibration wave generated in the elastic member 11 is basically the same as those of motors according to applications before the present application, and a detailed description thereof will be omitted.
In the prior art, however, since an amplitude of a vibration wave generated in the elastic member 11 is at most several microns, the flatness of a contact portion between the elastic member 11 and the frictional member 2a must be as large as the amplitude, resulting in an increase in working cost. If the contact portion has a poor flatness, contact states at opposing positions between the elastic member 11 and the frictional member 2a are considerably varied, resulting in a large rotation nonuniformity, and large noise.